Not Applicable.
This invention relates in general to radio positioning/navigation systems. More specifically and in particular, the present invention, hereinafter described in accordance with the current best mode of practice, is such a radio positioning/navigation system that integrates global navigation satellite systems (GNSS) with a time modulated ultra-wide band (TM-UWB) system to provide correlated positioning/navigation data either within a line-of-sight barrier, or in direct line of sight of GNSS beacons. In addition, the present invention overcomes the inherent problems of current radio positioning/navigation systems, such as multi-path signal propagation, the xe2x80x9cnear-farxe2x80x9d problem, and the attenuation of low power signals by a barrier.
A common need, and requirement of our society is to accurately track and record positions of aircraft, land vehicles, geographical landmarks, materials, buildings, animals, people, and other objects whether they are located indoors, out of doors, or moving in between. One method currently used to accomplish this goal uses radio positioning/navigation beacons and associated equipment. Radio positioning/navigation can be broadly defined as the use of radio waves to transmit information, which in turn can be received and utilized to determine position and to navigate. Some radio positioning/navigation systems either currently in use or under development, are LORAN, OMEGA, and global navigation satellite systems (GNSS) such as NAVSTAR, GLONASS (the Russian variant), and European systems (GNSS1, GNSS2, NAVSTAT and GRANAS). The radio positioning/navigation systems quickly becoming the standard worldwide are, Global Navigation Satellite Systems (GNSS) including the NAVSTAR Global Positioning System (GPS). The NAVSTAR GPS system is capable of providing real-time, three-dimensional position and navigation data.
The NAVSTAR GPS beacon system presently consists of twenty-four orbiting satellites, spaced in six separate circular orbits, with each accommodating four satellites. Of these, twenty-one are normally operational and three serve as spares. Each NAVSTAR GPS satellite reappears above the same ground reference approximately every twenty-three hours and fifty-six minutes. The spacing of satellites is designed to maximize probability that earth users will always have at least four satellites in good geometrical view for navigational use. The basic method of position determination via radio positioning and navigation signals is derived from the concept of triangulation. The term triangulation used herein refers to the general process of determining distance, a.k.a. range, from the present position to multiple known beacons, and mathematically solving for the point in space which satisfies these conditions. As applied to GNSS, the procedure requires calculation of signal travel time, which, when multiplied by the speed of light, renders distance.
A basic discussion of positioning/navigation as it relates to the NAVSTAR GPS is contained in a document entitled xe2x80x9cGPS NAVSTAR Global Positioning System, User""s Overviewxe2x80x9d, Reference Document YEE-82-009D, March 1991, prepared by ARINC Research Corporation. This document particularly describes the background of the NAVSTAR Global Positioning System, as well as technical descriptions, performance characteristics and actual user segments. As noted, this book was published in March 1991, and now nine years later the use of NAVSTAR GPS for practical commercial applications has grown immensely.
A process known as differential global positioning (DGPS or DGNSS) compensates for many of the errors which are common in radio positioning/navigation systems. An antenna at a known location receives line of sight (LOS) GNSS signals and broadcasts a signal with current correction adjustments for each satellite which can be received by any differential receiver within its signal range.
Location accuracy via GNSS is continually evolving. Standard GNSS receivers can typically produce position estimates within +/xe2x88x92100 meter accuracy. Sub-meter position accuracy of location can be achieved using DGNSS. Other techniques for improving accuracy are xe2x80x9cCarrier-phase GPSxe2x80x9d, xe2x80x9cWide Area Augmented GPSxe2x80x9d(WAAS), and GPS Interferometry.
GNSS relies on no visual, magnetic, or other point of reference which is particularly important in applications such as aviation and naval navigation that traverse polar regions where conventional magnetic navigational means are rendered less effective by local magnetic conditions. Magnetic deviations and anomalies common in standard radio positioning/navigation systems do not hinder GNSS. In addition, GNSS equipment is typically fabricated of standard, solid state electronic hardware, resulting in low cost, low maintenance systems, having few or no moving parts, and requiring no optics. GNSS does not have the calibration, alignment, and maintenance requirements of conventional inertial measuring units, and is available 24 hours per day on a worldwide basis.
During the development of the NAVSTAR GPS program, the United States Government made decisions to extend its use to both domestic and international communities. Its applications range from navigation over the land, in the air, and on the seas, to precision surveys, the tracking of trains and trucks, and even locating undetonated mines left behind in the 1991 Gulf War. As GNSS is rapidly becoming the accepted global standard for positioning/navigation applications when in direct line of sight of beacons, the following discussion focuses on GNSS.
One critical limitation of current GNSS systems is that the beacons are required to be in direct line of sight (LOS) of the receiver. In other words, if the GNSS receiver is used in heavily forested areas, in steep and narrow canyons, within a structure, adjacent to the outer walls of buildings, or behind various other line-of-sight barriers (LSB), the receiver will be unable to obtain a good repeatable reading, or in many cases, any reading at all. While GNSS systems have many important uses in wide open spaces, they are not useable within environments separated by line-of-sight barriers (LSB).
What is needed is a system that is globally correlated and provides repeatable, precise sub-centimeter positioning/navigation data for locating objects in direct line of sight (LOS) of GNSS beacons and within line-of-sight barriers (LSB). The result of such an all-encompassing system is accurate, consistent positioning and navigation data for a wide variety of applications that can be used both in direct line of sight (LOS) of GNSS beacons and within environments that do not allow these signals to penetrate.
In addition to the GNSS information discussed above, other related U.S. patents also deal exclusively with radio positioning/navigation within a line-of-sight barrier (LSB). Such references include, for example, U.S. Pat. No. 5,051,741 to Wesby, an invention directed to a system for locating the position of moveable elements in a wide area and U.S. Pat. No. 5,334,974 to Simms et al. which describes an invention that provides a fully automatic personal security system which combines the advantages of worldwide LORAN-C or GPS navigation with the substantially worldwide communication capabilities of a cellular telephone or communication satellite.
U.S. Pat. No. 4,918,425 to Greenberg et al. discloses an invention that provides a radio system and method for monitoring and locating objects, including individuals, animals and articles, both locally and globally using base stations communicating by ID code with portable transponders which are secured to the objects to be monitored. Another example is the device discussed in U.S. Pat. No. 5,311,185 to Hochstein et al, which is directed to a proximity detection device relying on a transponder that periodically transmits a signal. Transceivers are fixed at locations about a structure for receiving and transmitting signals to establish a location. U.S. Pat. No. 5,363,425 to Mufti et al. incorporates an identification badge having a radio frequency (RF) transmitter. Radio frequency (RF) receivers are located in telephones in various rooms of a structure. The location of the identification tag is determined to be the room with the nearest phone. Anders et al. in U.S. Pat. No. 4,656,463, proposes a passive transceiver tag which is sensed by an active transceiver. This proximity control system forms the basis for a location, identification, and measurement of movement of inventory system, commonly referred to as a LIMIS system.
A system that also addresses positioning and navigation within a line-of-sight barrier (LSB) is referenced in U.S. Pat. No. 5,952,958 to Speasl et al. It is an object of that invention to use GPS-Type RF signals within a line-of-sight barrier (LSB). The practicality of the above referenced patents using RF signals within a line-of-sight barrier (LSB) is limited due to associated problems encountered with multiple signal propagation paths (multi-path) and the xe2x80x9cnear-farxe2x80x9d problem discussed below.
Operation within a line-of-sight barrier (LSB) places fundamental limitations on the performance of radio positioning/navigation systems. The existence of multi-path with different time delays, gives rise to complex, time-varying transmission channels. A direct line-of-site path between beacons and receiver seldom exists within a line-of-sight barrier (LSB), because of interference or reflection from natural or man-made objects, and one must rely on the signal arriving via multi-path. Signals can be received within a line-of-sight barrier (LSB); however to date, the equipment required to mitigate and correct for multi-path remains complex, sophisticated and the process is not repeatable. These multi-path problems, in effect, limit the practical commercial use of radio transmission of positioning/navigation data within a line-of-sight barrier (LSB).
Another dilemma associated with radio transmission of positioning/navigation data within a line-of-sight barrier (LSB) is a phenomenon known as the xe2x80x9cnear-farxe2x80x9d problem. The near-far problem is due to simultaneous broadcasting of signals from multiple broadcast antennae. This problem arises because of the large variation of the user-to-broadcast antennae range. One advantage of using GNSS signals is that the average power being received from the GNSS satellite beacons remains approximately constant due to the large distance of the satellite beacons from the GNSS receiver(s). On the other hand in a local system, the broadcast antenna power from broadcast antennae varies a great deal, due to the inverse proportion to the square of the receiver""s distance from the broadcast antennae, and can overwhelm other incoming signals.
Although there have been attempts to use radio positioning/navigation signals within a line-of-site barrier, to date the use of this technology is commercially impractical because of the problems described in the previous discussions.
Departing radically from traditional RF techniques, ultra wideband (UWB) radio is a recent innovation in radio signal transmissions. Ultra wideband provides an innovative solution for local geo-positioning that overcomes multi-path and near-far problems.
A local positioning and navigation system using generic UWB timing signals to overcome multi-path and near-far problems is described in U.S. Pat. No. 6,054,950 to Robert J. Fontana, and is incorporated by reference in this disclosure. This patent teaches precise geolocation without the use of any tethered or cabled equipment, self-synchronization for pulse transmission wireless equipment to eliminate the need for additional cabling between units and a central processor unit (CPU) and a pulse transmission position measuring system including a system that employs self-synchronizing timing signals thereby obviating the need to use an external timing source for determining the position of an object. However, more sophisticated UWB signals are described in U.S. Pat. Nos. 5,952,956 and 5,363,108 to Fullerton et al., and in U.S. Pat. Nos. 5,832,035, 5,812,081, 5,677,927 to Fullerton and are also incorporated by reference. As described in these patents, a time-modulated, ultra-wide band (TM-UWB) system for telecommunications places individual pulses at very precise, repeatable time intervals and transmits the pulses across an ultra wideband spectrum. These digital pulses are low power, produce noise-like signals, are self identified by their timing sequence, and are capable of having data injected onto the timing sequence. The digital portion of this pulse technology allows for transmission of data, video, and voice at extremely high-speed transmission rates. The pulse-timing portion of this technology also provides for positioning and navigation. Radar applications are an additional use of this technology.
Historically, the only way to transmit radio signals such as voice, music, TV, data, etc., has been via continuously oscillating radio waves. Digital pulse technology, as referenced in U.S. Pat. Nos. 5,952,956 and 5,363,108 to Fullerton et al., and U.S. Pat. Nos. 5,832,035, 5,812,081, 5,677,927 to Fullerton transmits pulses of energy instead of waves. TM-UWB technology uses impulse transmitters to emit ultra-short xe2x80x9cGaussianxe2x80x9d monocycle pulses with a tightly controlled pulse-to-pulse interval. Most recently, IBM Microelectronics Corporation has developed two proprietary chips which are fabricated from advanced silicon germanium for use in TM-UWB transmitters and receivers. These chips precisely control pulsation timing and correlation to within a few trillionths of a second (pico-seconds). These monocycles are resistant to multi-path fading and provide extremely high data transmission rates. Each digital pulse can represent a 1 or a 0, and are not frequency dependent, hence they can be transmitted across a wide spectrum. TM-UWB pulse technology offers a viable solution to data transmission because it does not compete with the currently crowded radio wave spectrums. This technology provides a large number of operational capabilities beyond traditional oscillating radio wave transmission systems.
A basic discussion of impulse radio can be referenced in an article entitled xe2x80x9cImpulse Radio: How It Worksxe2x80x9d, published in IEEE Communications Letters, Vol. 2, No. Feb. 2, 1998. This article specifically explains the rationale for impulse radio technology, and the ability to employ this technology to solve many of the difficult problems encountered using wireless transmissions indoors. Additional discussions of the robustness of TM-UWB signal use can be referenced in an article entitled, xe2x80x9cUltra-Wide Bandwidth Signal Propagation for Indoor Wireless communicationsxe2x80x9d published in June 1997 by the EEE International Conference on Communications in Montreal, Canada.
TM-UWB technology has a number of beneficial characteristics. One is security. Due to the astounding number of possible combinations of timing sequences, it is statistically impossible to decode this type of transmission unless the required complex code is used by both transmitting and sending devices. Another by-product of the tremendous number of combinations is the unlikely chance for signal interference. The signals are so random and low powered that they are indistinguishable from background noise. Another beneficial characteristic of the system is that it operates at very low power spectral densities and does not need a power amplifier for signal transmission. TM-UWB systems consume substantially less power than existing conventional radios. Another beneficial characteristic of the system is that hardware is relatively simple to manufacture and costs substantially less than what is currently required to build spread spectrum radios and related equipment.
The TM-UWB system can provide local geopositions with sub-centimeter accuracy. This is achieved due to the precise timing of outgoing and incoming pulses. It is important to note that TM-UWB is not a global positioning/navigation system. Although multi-mile ranges are capable with this technology, it does not provide global integration with GNSS positioning/navigation systems.
Therefore, there is a common need in society for a system that utilizes both GNSS and TM-UWB technologies to provide positioning/navigation capabilities both in direct line of sight (LOS) of GNSS beacons, and within a line-of-sight barrier (LSB) using TM-UWB beacons. None of the geopositioning systems discussed in the prior art meet these needs because they are either 1) local systems only, 2) imprecise, 3) do not work indoors and outdoors, or 4) are not cost effective due to multi-path and near-far problems.
The present invention provides a system for utilizing two positioning and navigation systems in a single unit which may be used within sight of earth-orbiting GNSS satellites as well as behind a line-of-sight barrier obstructing the earth-orbiting satellites. A receiver/processor which is mobile, such as might be carried on a forklift in a warehouse with indoor and outdoor storage areas, includes a GPS receiver which receives and develops navigation and position information from the signals transmitted by the system of earth-orbiting satellites. The receiver/processor also includes a TM-UWB receiver capable of receiving transmissions from a group of at least three ground-based beacons stationed at precise known locations, each of which independently transmits a distinct TM-UWB signal, including timing and location information. The receiver/processor is provided with programmable memory which holds coordinates of the space in which the TM-UWB receiver is to be utilized to develop location and navigation information to the exclusion of the GPS receiver of the unit. A first antenna exterior to any line-of-sight barrier behind which the receiver/processor will be operated, that is, atop the building in which the mobile receiver/processor is to be used, collects signals from the earth-orbiting GNSS satellites and passes the collected signals through the roof or other line-of-sight barrier to a second antenna which rebroadcasts the collected signals.
The receiver/processor receives the retransmitted satellite data signals while behind the line-of-sight barrier, (e.g. within the building) such that the GPS receiver will remain active and will not need a period of warm-up once the mobile receiver/processor leaves the building and may receive signals directly from the earth-orbiting satellites. The onboard storage is interrogated by the receiver/processor to determine when the receiver/processor has left the space in which the GNSS signals received are to be disregarded. Hereinafter, separation by a line of sight barrier is referred to as xe2x80x9cwithin a line-of-sight barrierxe2x80x9d (LSB).
The present invention also provides a cost effective method for overcoming problems associated with multiple signal propagation paths and relative proximity of simultaneously transmitting antenna within a line-of-sight barrier (LSB). None of the geopositioning systems discussed in the prior art meet these needs because they have one or more of the following shortcomings 1) local systems only, 2) imprecise, 3) do not work indoors and outdoors, 4) are not cost effective due to multi-path and near-far problems, 5) require synchronization of timing signals from multiple beacons, or 6) rely solely on a single use timing signal.
The present invention differs from the systems described in the prior art because it is a comprehensive system for precise, global positioning and navigation, both in direct line-of-sight (LOS) of GNSS beacons and within a line-of-sight barrier (LSB). The present invention utilizes TM-UWB telecommunication pulses as a timing signal which is a cost effective method for overcoming problems associated with multi-path and near-far within a line-of-sight barrier (LSB). The present invention does not deal with real-time kinematic position and navigation solutions, and therefore does not require synchronization of timing signals from multiple beacons.
Globally, in direct line of sight (LOS) of GNSS beacons, the present invention utilizes GNSS ephemeris and pseudo-random noise signals to determine positioning and navigation information. Current ephemeris and GNSS system operational status is relayed via GNSS re-radiation antennae located within the line-of-sight barrier (LSB). This information is necessary to keep the GNSS receiver portion of the receiver/processor activated for applications in direct line of sight (LOS) of GNSS beacons. Optional correction signals from a DGNSS differential antenna and receiver may be used to enhance accuracy.
Locally, within a line-of-sight barrier (LSB), the present invention utilizes TM-UWB pseudo-random noise signals to determine positioning and navigation information. The term xe2x80x9clocallyxe2x80x9d as it is used herein, refers to the part of the system that can be used indoors and outdoors within the multi-mile range of TM-UWB beacons. TM-UWB beacons may be located within, or outside a line-of-sight barrier (LSB). The TM-UWB beacons must be non-coplanar, in order to determine altitude. The receiver/processors and TM-UWB beacons are parts of a system which communicate with each other in order to determine positioning and navigation data locally. The present invention integrates and correlates GNSS and TM-UWB positioning and navigation data into a seamless format.
The present invention specifically includes receiver/processors, TM-UWB beacons at known locations, GNSS signal re-radiation antennae, and an optional host computer which can provide enhanced information services. A receiver/processor includes a GNSS receiver/processor, a TM-UWB receiver/processor, a micro-processor with solution software to integrate and correlate GNSS and TM-UWB positioning and navigation data memory, and a wireless data link to communicate with other receiver/processors and optional host computer. The receiver/processor may be contained in such devices as, but not limited to, an RFID tag, a cell phone, a computer, or a personal digital assistant (PDA).
The present invention provides positioning and navigation information by utilizing GNSS and/or TM-UWB signals which are processed geometrically using triangulation and/or tri-lateralization techniques which yield positioning and navigation data. The receiver/processor also uses a wireless data link to communicate with other receiver/processors, or with an optional host computer. The optional host computer is used to store, calculate, and deliver enhanced positioning and navigation information for various applications.
It is an object of the present invention to utilize TM-UWB technology for determining the positions of objects locally.
It is another object of the present invention to utilize TM-UWB technology for determining the positions of objects within a line-of-sight barrier.
It is a further object of the present invention to utilize TM-UWB to overcome problems such as multi-path signal propagation, and the xe2x80x9cnear-farxe2x80x9d problem associated with current radio positioning/navigation systems.
It is a further object of the present invention to integrate and correlate the position/navigation information from both GNSS systems and a TM-UWB system for locating objects.
It is a further objection of the invention to provide a system which may provide location and navigation information to a moving object on a real-time basis by using either a time-multiplexed ultra wide band data transmission scheme or the GNSS system or both, whether the objection is moving within the line of sight of GNSS satellite or not. These and other objects will be better understood from review of the detailed description which follows and in which the following definitions are applicable.
Global Navigation Satellite System (GNSS)xe2x80x94A generic term for specific systems such as the Russian GLONASS and the United States NAVSTAR GPS, utilizing equipment which receives signals from a relevant constellation of navigational satellites in earth orbit.
NAVSTAR Global Positioning System (NAVSTAR GPS)xe2x80x94The United States Government""s satellite navigation system which broadcasts time and ranging data globally. Designed to provide a highly accurate, reliable, continuous 24-hour, worldwide coverage for position reporting and navigation.
Differential Global Positioning System (DGPS) or Differential Global Navigation Satellite System (DGNSS)xe2x80x94A positioning system which also includes an antenna that is precisely surveyed to a known location. The antenna receives GPS signals and broadcasts current correction data for each satellite which can be received by a DGPS antenna. Location accuracy within one meter can be achieved.
Line-of-Sightxe2x80x94(LOS) Unobstructed linear signal path between radio positioning/navigation transmitters and receiving antennae.
Line-of-Sight Barrierxe2x80x94(LSB) Any barrier, solid or non-solid, that restricts direct linear receipt of any radio positioning/navigation signal.
Locallyxe2x80x94Refers to the part of the system that can be used indoors and outdoors within the multi-mile range of TRADEMARK-UWB beacons.
Time Modulated Ultra-Wide Band (TRADEMARK-UWB)xe2x80x94System that transmits very low power radio signals with very short pulses using very wide signal bandwidths. The pulses are transmitted at ultra precise, nearly random intervals, and frequencies to convey data using a technique called pulse position modulation.
Ultra Wide Bandxe2x80x94System that transmits very low power radio signals with very short pulses using very wide signal bandwidths.
Beaconxe2x80x94A device that emits radio signals for positioning/navigation purposes. Radio Frequency (RF)xe2x80x94Radio transmission of data.
Receiverxe2x80x94Hardware that is capable of receiving either GNSS or TRADEMARK-UWB radio positioning/navigation signals
Transceiverxe2x80x94Hardware that is capable of receiving and transmitting radio positioning/navigation signals or data from either GNSS or TRADEMARK-UWB systems.
Geographical Information System (GIS)xe2x80x94Any information system that is designed to work with data referenced by spatial or geographic coordinates. A GIS is both a database system with specific capabilities for spatially-referenced data, as well as a set of operations for mapping and analyzing the data.
Wide Area Augmentation System (WAAS)xe2x80x94A system where a network of ground reference stations monitors GNSS satellite signals and passes the information to a Master Station. The Master Station uplinks correction data to Geo-stationary satellites (not the GNSS navigation satellites) which in turn downlink the correction data to a user""s GNSS receiver. This system is designed to improve integrity, accuracy, availability, and continuity of service, with a view to accuracy being compatible with aircraft approach and landing aids, and other uses where such accuracy is required.
Triangulationxe2x80x94Any mathematical procedure to calculate position based on the intersection of ranges from known points (includes all variations such as tri-lateralization and resection, etc., whether or not angles, per se, are used).